With the winter's second blizzard raging outside, Cliff Asness sat in his relatively modest office in Greenwich, Connecticut, surrounded by three of his partners, his PR guru, an impressive collection of unread books, and a sea of foot-tall hard-plastic replicas of Spiderman, the Incredible Hulk, and friends. "Let me be technical," he said. "It all sucked."

Asness--intense, bald, and bearded, with a $500 million fortune and a doctorate in finance--was reflecting on the dark days of 2008, when capitalism seemed to be imploding, when Bear Stearns and Lehman Brothers had collapsed and the government had hastily arranged bailouts of Merrill Lynch, Morgan Stanley, Goldman Sachs, and AIG, among others.

His own business, Applied Quantitative Research--one of the world's leading quantitative-investment, or "quant," funds--had also suffered painfully. The money his team managed fell to $17.2 billion in March 2009, from a peak of $39.1 billion in September 2007, as clients headed for the exits with what was left of their cash.

Such losses can be fatal for fund managers like AQR, since sophisticated investors pay them big fees for exceptional performance and, understandably, have little patience for anything less. As AQR's founders felt the tremors from Wall Street rippling through their offices, Asness said, "we worried about the stability of the financial sector, the stability of the economy, and the stability of society." To Bloomberg Markets magazine, last fall, he was even more explicit: "I heard the Valkyries circling. I saw the Grim Reaper at my door."

Yet they survived. And AQR--which makes its fortune, like other quants, by using high-speed computers and financial models of extraordinary complexity--has made a stupendous recovery in the past two years.